1. Field of the Invention
The present invention relates to an optical diaphragm apparatus, and particularly to a small size optical diaphragm apparatus.
2. Description of the Related Art
In endoscope apparatuses in which a solid imaging device is used, using an optical system of a fixed focus and a fixed diaphragm has hitherto been common. At the same time, with a progress in a semiconductor manufacturing technology, a solid imaging device which has fine pixels has been applicable even in an endoscope. Such a solid imaging device of fine pixels is sensitive to a change in a focal position due to a distance up to an object to be photographed. In observation and examination by an endoscope apparatus, it is difficult to maintain a constant distance all the time from an object to be photographed such as a wall surface of a body cavity and a diseased part. Therefore, in an endoscope apparatus which includes a conventional optical system, it has been difficult to obtain a high-definition image in which peculiarities of minute pixels are fully exploited.
For avoiding this problem, the following two methods (1) and (2) are available.    (1) A method of adding a focusing function which displaces a part of a lens, or an entire lens in accordance with a distance from the object to be photographed.    (2) A method in which an optical system is let to be a fixed focus, and focusing has been performed to have a proper image formation with respect to an object to be photographed at a far point, and a satisfactory image formation is achieved by increasing a depth of focus (focal depth) by reducing an aperture diameter at a time of near point photography.
In a case of the method (2) mentioned above, a variable diaphragm mechanism is necessary. Therefore, there is a problem that a quantity of light reaching the solid imaging device at the time of near point photography is decreased. Here, in an endoscope in which a picture is normally taken by light of an illuminating unit at a front end section, it is possible to secure a sufficient quantity of light at the time of near point photography. Therefore, the decrease in the quantity of light at the time of the near point photography does not become a major problem.
Thus, in the endoscope apparatus, for making a full use of a capacity of the imaging device of minute pixels, at least one of a lens driving unit and a variable diaphragm unit is required. From a point of view of an optical efficiency, method (1) is excellent. However, it is quite difficult to incorporate the lens driving unit in an endoscope of a small diameter.
Therefore, for the endoscope of a small diameter, it is desirable to use an ultra small variable diaphragm apparatus. An example of the ultra small variable diaphragm apparatus which can be used in an endoscope is proposed for example, in Japanese Patent No. 3204793.
A structure disclosed in Japanese Patent No. 3204793 will be described below by referring to FIG. 21 and FIG. 22. A rotating disc 36 in a form of a ring which rotates around an optical axis L as a center is provided. A movable object 37 is provided on one surface of the rotating disc 36. A stacked-layered piezoelectric element 38 is mounted on and fixed to the movable object 37.
An axial direction of expansion and contraction of the piezoelectric element 38 is set up toward a tangential direction of a virtual circle with the optical axis L as a center. The piezoelectric element 38 is disposed inside a groove 40 which is formed in a piezoelectric element frame 39.
The movable object 37 is integrated with the rotating disc 36 to form an essential rotating movable object. Moreover, the movable object 37 is installed so as to slide upon being pressure-welded on a wall surface of a frame 41 of a lens barrel 21. Furthermore, the circulating disc 36 is installed so as to slide upon being pressure-welded also on a wall surface of the piezoelectric element frame 39. Thus, the piezoelectric element frame 39 and the frame 41 of the lens barrel 21 form an integrated stationary member. Accordingly, the rotating disc 36 can be rotated by applying a drive voltage as mentioned above, to the piezoelectric element 38.
A diaphragm blade 35 is formed by disposing three blade members at same interval. Each diaphragm blade 35 is pushed by a diaphragm pushing member 40a. Moreover, an intermediate portion of each diaphragm blade 35 is pivoted by a supporting pin 41a which is erected in the diaphragm pushing member 40a. 
A rear end of the diaphragm blade 35 is connected to a driving pin 42 which is erected in the rotating disc 36. When the rotating disc 36 rotates, the diaphragm blade 35 rotates around the supporting pin 41a as a center. Accordingly, it is possible to adjust an aperture value.
A guide hole 44 in which a pin 43 which is erected between the piezoelectric element frame 39 and the diaphragm pushing member 40 is fitted, is provided in the rotating disc 36. Moreover, a movement of the pin 43 is regulated by both ends of the guide hole 44, and a range of rotation of the rotating disc 36 is regulated.
A variable diaphragm such as the one mentioned above is used in small size piezoelectric vibrators. Accordingly, as compared to a variable diaphragm using an electromagnetic actuator which is used in a normal still camera, it is possible to reduce the size substantially. Therefore, it is easily applicable in an endoscope of a comparatively thicker diameter.
However, there are limitations on a size reduction of a stacked-layered piezoelectric vibrator, which is necessary for achieving a displacement amount in an inertial drive. Furthermore, for driving the diaphragm, a rotating plate linked to the diaphragm blade becomes necessary. Therefore, it is difficult to use the stacked-layered piezoelectric vibrator in an endoscope of a small diameter.